earth would not be able to produce so many rivers unless it poured them from a copious reserve. This being so, sometimes below the earth a river must become swollen, 4 and leaving its banks assail with violence all obstacles that meet it. So there will be a movement of some point on which the river has made an onset, and which it will keep lashing until its waters fall. Or it may happen that the constant wear of a stream may eat away some quarter, dragging down thereby some mass above, by whose fall, in turn, the surface which rested on it is shaken. Now surely a man trusts too 5 much to the sight of the eyes and cannot launch out his imagination beyond, if he does not believe that the depths of earth contain a vast sea with winding shores. I see nothing to prevent or oppose the existence of a beach down there in the obscurity, or a sea finding its way through the hidden entrances to its appointed place. There, too, it occupies as much space as here, perhaps more, since the regions up on earth have had to be shared with so many living creatures; but the hidden regions being desert without inhabitant give freer scope to the waves of the nether ocean. And who is there to hinder the sea from 6 swelling there and being tossed by all the winds that every interstice of the earth, and every species of atmosphere can create? So, then, when a storm greater than ordinary has arisen, it may beat upon some one side of the earth with too great vehemence and move it. For on the surface likewise, many places which had been far from the sea have felt the violence of its sudden approach: villas almost out of sight of it have been invaded by the waves which used only to be heard in the distance. The nether sea, too, can approach and retire; neither of which movements can take place without shock to the earth that stands above it. VIII I do not, indeed, suppose that you will long hesitate to believe that 1 there are underground rivers and a hidden sea. From what other cause could the rivers burst out and come to the surface unless the source of the moisture were shut up within the earth? For instance, when one sees the Tigris interrupted and dried up in the middle of its course, not diverted as a whole, but gradually with imperceptible losses first lessen and then waste away, where do you suppose it goes to if not to the depths of the earth, especially as you see it emerge again not less in volume than its former stream? And what are you to say when you 2 see the Alpheus, so celebrated by the poets, sink in Achaia and, having crossed beneath the sea, pour forth in Sicily the pleasant fountain Arethuse? And don’t you know that among the explanations given of the occurrence of the inundation of the Nile in summer, one is that it bursts forth from the ground, and is swollen not by rain from above but by water given out from within the earth?